Engine cooling device

ABSTRACT

An engine cooling device includes: a water pump pressure-feeding a common coolant to plural coolant circulation paths; an engine including an engine main body; a water-cooled header cooling an exhaust system of the engine by use of the coolant, a heat capacity of the water-cooled header being smaller than that of the engine main body; an ECU and a thermostat determining whether or not the coolant is allowed to flow through the fifth and sixth coolant circulation paths among the plural coolant circulation paths on the basis of a given determination value. The given determination value relates to an amount of heat transferred from the exhaust gas to the water-cooled header.

TECHNICAL FIELD

The present invention relates to an engine cooling device. More particularly, the present invention relates to an engine cooling device that includes an exhaust system cooling portion cooling an exhaust system of an engine by the use of a common cooling medium flowing through a main body of the engine.

BACKGROUND ART

Conventionally, there are known technologies to cool an exhaust system of an engine (specifically, for example, an exhaust manifold) by the use of a cooling medium such as water. For example, Patent Document 1 describes a technology that may relate to the present invention. Patent Document 1 describes an exhaust manifold device including: a water jacket provided around an exhaust manifold; and a water injection means to inject water in the state of spraying water to the water jacket. Additionally, as another technology that may relate to the present invention, for example, Patent Document 2 describes a cooling control device of an internal combustion engine including flow rate control valves which can respectively change the ratios of the supply of the cooling media to plural cooled portions. Specifically, Patent Document 2 describes the cooling control device of the internal-combustion engine including the flow control valves which are respectively provided in coolant paths leading the coolant to the plural cooled portions such as exhaust ports.

-   Patent Document 1: Japanese Unexamined Patent Application     Publication No. 63-208607 -   Patent Document 2: Japanese Unexamined Patent Application     Publication No. 2007-132313

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Incidentally, the exhaust emission is demanded to be reduced for dealing with environmental problems. In order to reduce the exhaust emission in a low- or middle-load driving state, there is a technique of arranging a three-way catalyst near the engine to immediately warm the three-way catalyst.

On the other hand, in order to reduce the exhaust emission in a high-load driving state during the employment of the above technique, it is preferable that the engine is driven at the theoretical air-fuel ratio or the proximity thereof. However, the arrangement of the catalyst near the engine may overheat the catalyst. Thus, as a result, the degradation in the exhaust emission is worried due to the excessive degradation of the catalyst. Therefore, in light of the reduction in exhaust emission in the high-load driving region, the three-way catalyst has to be arranged apart from the engine. However, the reduction in exhaust emission may be insufficient in the low and middle-load driving region where the catalyst is immediately warmed. This needs an increased amount of noble metals accelerating the purging of the catalyst. However, these noble metals are rare, and the cost might be increased in this case.

Under the above circumstances, in order to achieve reduction suitably in both of the exhaust emission in the low- and middle-load driving region where the catalyst is immediately warmed and the exhaust emission in the high-load driving region, the exhaust system can be cooled with a cooling medium to reduce the exhaust temperature. This can suppress the overheating of the catalyst. This allows the catalyst to be arranged near the engine, thereby achieving reduction suitably in both of the exhaust emission in the low- and middle-load driving region where the catalyst is immediately warmed and the exhaust emission in the high-load driving region.

On the other hand, in cases where the exhaust system is cooled with the cooling medium, it is rational to commonly use the cooling medium (for example, a long-life coolant as cooling water for an engine) flowing through the engine main body in light of cost or the like. Generally, the cooling medium flowing through the engine main body is cooled by a cooler (for example, a radiator). Generally, whether or not the cooling medium flows through the cooler is determined on the basis of the temperature of the cooling medium flowing through cooling medium circulation paths including the engine main body.

However, there is a partial variation in temperature of the cooling medium flowing through the cooling medium circulation paths. For this reason, whether or not the cooling medium flows through the cooler is determined on the basis of the temperature of an outlet of the engine main body or the temperature of the cooling medium just after flowing out of the engine main body. Such a determination can prevent or suppress the damage of the engine caused by the overheating of the cooling medium.

However, in cases where there is provided an exhaust system cooling portion for cooling the exhaust system by the use of the common cooling medium flowing through the engine main body, the heat capacity of the exhaust system cooling portion is smaller than that of the engine main body, because the size of the cooling portion for cooling the exhaust system is typically smaller than that of the engine main body. Therefore, in cases where the exhaust system cooling portion is provided, the influence of the transferred heat on the exhaust system cooling portion is greater than that of received heat on the engine main body, in light of the cooling medium flowing therethrough. When whether or not the cooling medium flows through the cooler is determined as mentioned above in this case, the temperature of the cooling medium in the exhaust system cooling portion with a small heat capacity may be higher than a suitable temperature before actually flowing through the cooler. Therefore, the overheating or the boiling may happen. This is a problem that the engine may be damaged.

Thus, the present invention has been made in view of the circumstances and has an object to provide an engine cooling device that can prevent or suppress damage of an engine due to overheating or boiling of cooling medium in an exhaust system cooling portion for cooling an exhaust system of an engine, in the case of provision of the exhaust system cooling portion for cooling the exhaust system with the cooling medium flowing through an engine main body.

Means for Solving the Problems

An engine cooling device to solve the above problem includes: a cooling medium pressure-feeding portion feeding a common cooling medium to plural cooling medium circulation paths; an engine including an engine main body incorporated into at least one of the plural cooling medium circulation paths; an exhaust system cooling portion incorporated into at least one of the plural cooling medium circulation paths, and cooling an exhaust system of the engine by the use of the coolant, a heat capacity of an exhaust system cooling device being smaller than that of the engine main body; a cooler incorporated into at least one of the plural cooling medium circulation paths, and cooling the coolant; a flow control device determining whether or not the cooling medium flows through the at least one of the plural cooling medium circulation paths into which the cooler is incorporated on the basis of a given determination value, and controlling flowing of the cooling medium, wherein the given determination value relates to an amount of heat transferred from the exhaust gas to the cooling medium in the exhaust system cooling portion.

The engine cooling device may further include a flow rate adjusting portion incorporated into at least one of the cooling medium circulation paths into which the exhaust system cooling portion is incorporated, among the plural cooling medium circulation paths, and adjusting a flow rate of the cooling medium discharged from the exhaust system cooling portion such that a pressure force of the cooling medium flowing through the exhaust system cooling portion is greater than a system pressure force of the cooling medium flowing through each of the plural cooling medium circulation paths.

Effects of the Invention

The present invention prevents or suppresses damage of an engine due to overheating or boiling of a cooling medium in an exhaust system cooling portion for cooling an exhaust system of an engine, in the case of provision of the exhaust system cooling portion for cooling the exhaust system with the cooling medium flowing through an engine main body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an engine cooling device (hereinafter, simply referred to as cooling device) 100 according to the present embodiment, in FIG. 1, pipes defining a coolant circulation path in the cold state in which a thermostat 60 is closed are illustrated by dashed lines, whereas pipes defining a coolant circulation path in the warm state in which the thermostat 60 is opened are illustrated by solid lines, and in addition, circulation directions of the coolant W are illustrated by arrows, such definitions are applicable to FIGS. 3-8;

FIG. 2 is a schematic view of a water-cooled exhaust manifold (hereinafter simply referred to as water-cooled header) 30;

FIG. 3 is a view of a first coolant circulation path 81;

FIG. 4 is a view of a second coolant circulation path 82;

FIG. 5 is a view of a third coolant circulation path 83;

FIG. 6 is a view of a fourth coolant circulation path 84;

FIG. 7 is a view of a fifth coolant circulation path 85;

FIG. 8 is a view of a sixth coolant circulation path 86;

FIG. 9 is a schematic view of a specific configuration of an ECU 1;

FIG. 10 is a view of an increase in coolant temperature THW with a change in rotational number NE and a change in vehicle speeds SPD, the coolant temperatures THW are indicated by a solid line in the case of the cooling device 100 and by a dashed line in the case of a cooling device 100X in FIG. 10, and the cooling device 100X is substantially similar to the cooling device 100, except that the cooling device 100 x is not provided with the water-cooled header 30;

FIG. 11 is a view of flow rate of the coolant W flowing through the water-cooled header 30 in accordance with the opening and closing of the thermostat 60;

FIG. 12 is a flowchart of the operation of the ECU 1;

FIG. 13 is a schematic view explaining the control to forcibly open the thermostat 60;

FIG. 14 is a view of the flow rate of the coolant W flowing through the water-cooled header 30 by a solid line in the warm state in the cooling device 100 and by a dashed line in a cooling device 100Y substantially similar to the cooling device 100, except that the cooling device 100Y is not provided with an orifice 70; and

FIG. 15 is a view of a change in inlet pressure P1 and a change in outlet pressure P2 of the water-cooled header 30 at high-temperature test, together with a change in vehicle speed SPD, a change in water temperature THW, and a change in rotational number NE.

BEST MODES FOR CARRYING OUT THE INVENTION

An embodiment according to the present invention will be described later in detail with the accompanied drawings.

A cooling device 100 will be explained with reference to FIGS. 1-9. The cooling device 100 includes: an ECU (Electronic Control Unit) 1; a water pump 10; an engine 20; a water-cooled header 30; a heater core 40; a radiator 50; a thermostat 60; and an orifice 70. The water pump 10 is installed in the engine 20. The water pump 10 is a mechanical pump driven by the output of the engine 20, and pressure-feeds coolant W as a cooling medium.

The engine 20 has an engine main body 21. The engine main body 21 includes a cylinder head and a cylinder block not illustrated. The engine main body 21 is formed with a water jacket 22, a bypass path 23, and a communication path 24. The coolant W flows through the water jacket 22. The coolant W has flowed through the water pump 22 cools the engine main body 21. The Bypass path 23 permits the coolant W to flow to the thermostat 60 from the water jacket 22. Specifically, the bypass path 23 communicates the outlet side of the water jacket 22 with the outside thereof. The communication path 24 communicates the inlet side of the bypass path 23 with the outside thereof. The engine main body is provided with a water temperature sensor 91 detecting a water temperature THW being a temperature of the coolant W, and an engine rotational number sensor 92 detecting a rotational number NE of the engine 20. The water temperature sensor 91 is provided at the outlet side of the water jacket 22 to detect the coolant temperature THW.

The water-cooled header 30 is installed in the engine main body 21. The water-cooled header 30 allows the exhaust gas exhausted from the cylinders of the engine 20 to converge. As illustrated in FIG. 2, the water-cooled header 30 includes an outer wall portion 302 covers the entirety of plural exhaust pipes 301. A coolant flowing path is defined between the outer wall portion 302 and the plural exhaust pipes 301. In the water-cooled header 30, the coolant W is supplied to the coolant flowing path via a coolant inlet 303, and is discharged from the coolant flowing path via a coolant outlet 304. In the present embodiment, the water-cooled header 30 corresponds to an exhaust system cooling portion.

Returning to FIG. 1, heat is exchanged between the heater core 40 and the coolant W. The heater core 40 is used in an air conditioner not illustrated. The air conditioner functions as a heater to send air warmed by the heater core 40 into the vehicle interior. The radiator 50 promotes the heat radiation from the flowing coolant W with the wind generated by running or by an electric fan not illustrated, thereby cooling the coolant W. In the present embodiment, the radiator 50 corresponds to a cooler.

The thermostat 60 is closed in the cold state and is opened in a warm state, thereby controlling the flow of the coolant W. Also, the thermostat 60 with the ECU 1 determine whether or not the coolant W flows through the radiator 50 on the basis of a given determination value, and controls the flow of the coolant W. This given determination value relates to a cooling loss Qw described later. The thermostat 60, specifically, under the control of the ECU 1, allows the coolant W to flow via the radiator 50, when the cooling loss Qw is equal to or more than a given determination value, thereby controlling the flow of the coolant W. Specifically, the thermostat 60, under the control of the ECU 1, is forcibly opened, when the cooling loss Qw is equal to or more than a given determination value. This allows the coolant W to flow via the radiator 50. The orifice 70 adjusts the flow rate of the coolant W. The flow rate of the orifice 70 is fixed as a constant value, and decreases the flow rate of the coolant W by a given amount only.

The cooling device 100 includes coolant circulation paths 81 to 86 corresponding to the first to sixth cooling medium circulation paths. The first, second, and third coolant circulation paths 81, 82, and 83 are circulation paths through which the coolant W flows when the thermostat 60 is closed. Also, fourth, fifth, and sixth coolant circulation paths 84, 85, and 86 are circulation paths through which the coolant W flows when the thermostat 60 is opened. The water pump 10 pressure-feeds the common coolant W to these coolant circulation paths 81-86. In the present embodiment, the water pump 10 corresponds to a cooling medium pressure feeding device.

The water pump 10, the engine 20, the water-cooled header 30, the heater core 40, the radiator 50, the thermostat 60 or the orifice 70 is incorporated appropriately into the plural coolant circulation paths 81 to 86. As for the coolant circulation paths 81 to 86, each of them are connected to one another directly or indirectly via pipes. Next, the coolant circulation paths 81 to 86 will be described in detail with reference to FIGS. 3 to 8.

The water pump 10, the engine main body 21, the heater core 40, and the thermostat 60 are incorporated into the first coolant circulation path 81, and in addition, the coolant W flows in this order. The coolant W also flows through the engine main body 21, that is, the water jacket 22. The water pump 10, the engine main body 21, and the thermostat 60 are incorporated into the second coolant circulation path 82, and the coolant W flows in this order. Also, when the coolant W flows through the engine main body 21, the coolant W flows through the water jacket 22 and the bypass path 23 in this order. Specifically, the water pump 10, the water-cooled header 30, the engine main body 21, and the thermostat 60 are incorporated into the third coolant circulation path 83, so that the coolant W flows through the circulation path in this order. Also, the coolant W flows through the engine main body 21, that is, the communication path 24 and the bypass path 23 in this order. The radiator 50 is not included in the first-third coolant circulation paths 81 to 83.

Specifically, the water pump 10, the engine main body 21, the heater core 40, and the thermostat 60 are incorporated into the fourth coolant circulation path 84, and the coolant W flows the fourth coolant circulation path 84 in this order. Also, when the coolant W flows through the engine main body 21, the coolant W flows through the water jacket 22. The water pump 10, the engine main body 21, the radiator 50, and the thermostat 60 are incorporated into the fifth coolant circulation path 85, and the coolant W flows through the fifth coolant circulation path 85 in this order. Also, when the coolant W flows through the engine main body 21, the coolant W flows through the water jacket 22. The water pump 10, the water-cooled header 30, the orifice 70, the radiator 50, and the thermostat 60 are incorporated into the sixth coolant circulation path 86, and the coolant W flows through the sixth coolant circulation path 86 in this order. In the coolant circulation paths 81 to 86 configured above, the coolant W flows through the water-cooled header 30 when the thermostat 60 is opened and closed (in other words, when the coolant W flows through the radiator 50 and does not therethrough).

As illustrated in FIG. 8, the orifice 70 is provided on the downstream side of the water-cooled header 30 and on the front side of the radiator 50 in the sixth coolant circulation path 86 in which where the water-cooled header 30 is installed. More specifically, the orifice 70 is provided on the downstream side of the water-cooled header 30 and on the front side of the joining point of the fifth coolant circulation path 85 that is the other one. The orifice 70 reduces the flow rate of the coolant W only by a given amount to adjust the flow rate of the coolant W discharged from the water-cooled header 30 such that the pressure of the coolant W that has flowed through the water-cooled header 30 is higher than a system pressure of the plural coolant circulation paths 81 to 86. Specifically, this system pressure corresponds to the pressure of a radiator cap of the radiator 50. In the present embodiment, the orifice 70 corresponds to a flow rate adjusting portion.

As illustrated in FIG. 9, the ECU 1 includes: a microcomputer including a CPU 2, a ROM 3, and a RAM 4; and input-output circuits 5 and 6. The CPU 2, the ROM 3, the RAM 4, and the input-output circuits 5 and 6 are connected to one another by a bus 7. The ECU 1 mainly controls the engine 20. Specifically, the ECU 1 controls fuel injection valves not illustrated. Also, in addition to this, the ECU 1 controls the thermostat 60. These controlled objects are electrically connected to the ECU 1.

Also, the ECU 1 is electrically connected to various sensors such as a water temperature sensor 91, the engine rotational number sensor 92, an air flow meter 93 (more specifically, an intake air quantity sensor 93 a and an intake air temperature sensor 93 b). The cooling water temperature THW, the rotational number NE, and the intake air quantity GA and the intake air temperature THA are detected by the ECU 1 on the basis of the output of the water temperature sensor 91, the output of the engine rotational number sensor 92, and the output of the air flow meter 93, respectively. The ROM 3 stores map data and programs describing various processes performed by the CPU 2. The CPU 2 performs the processes while utilizing a temporary memory area of the RAM 4 if necessary on the basis of the programs stored in the ROM 3. This functionally achieves a control portion, a determination portion, a detection portion, a calculation portion, and the like in the ECU 1.

The ECU 1 functionally achieves the detection portion detecting plural estimation factors including the intake air quantity GA of the engine 20, and the estimation portion estimating the cooling loss Qw which is the amount of the heat transferred to the cooling medium from the exhaust gas in the water-cooled header 30 on the basis of the estimation factors detected by the detection portion. The cooling loss Qw can be used for detecting whether or not the driving state of the engine 20 is in the high-load driving state. The reason why the above-mentioned plural estimation factors include the intake air quantity GA is that the intake air quantity GA and the cooling loss Qw highly linearly correlate to each other. Further, it is desirable that the above-mentioned plural estimation factors further include at least one of the coolant temperature THW which is a cooling medium temperature, the intake air temperature THA, and the rotational number NE. This is because these four factors significantly influence on the cooling loss Qw.

The cooling loss Qw changes as the driving environmental condition of the engine 20 such as the initial state changes. In contrast, the coolant temperature THW and the intake air temperature THA can indicate the driving environmental condition of the engine 20. Also, the heat generated from the engine 20 increases as the friction of the engine 20 increases, whereby the cooling loss Qw tends to increase. In contrast, the rotational number NE can indicate the degree of the friction of the engine 20. For this reason, to estimate the cooling loss Qw with high accuracy, it is desirable that the plural estimation factors further include at least one of the coolant temperature THW, the intake air temperature THA, and the rotational number NE.

It is the most desirable that the cooling loss Qw should be estimated based on the next formula (1) including all of these four factors.

Qw=(THW+THA)×NE×GA  formula (1)

In other words, it is the most desirable that the cooling loss Qw should be estimated based on a value calculated by multiplying the rotational number NE, the intake air quantity GA, and the sum of the coolant temperature THW and the intake air temperature THA. This is because when the cooling loss Qw estimated by the formula (1) in test according to an experiment, most highly correlates linearly to the actual cooling loss Qw. For this reason, specifically, the ECU 1 estimates the cooling loss Qw based on the formula (1).

Also, the ECU 1 functionally achieves the control portion which determines whether or not the coolant W is allowed to flow through the radiator 50 on the basis of a given determination value concerning the cooling loss Qw. Specifically, the control portion is functionally achieved to control the thermostat 60 to allow the coolant W to flow via the radiator 50 when the cooling loss Qw meaning the estimated amount of the transferred heat is equal to or more than a given determination value. In this regard, in the present embodiment, the control portion is functionally achieved to forcibly open the thermostat 60 under the conditions where the cooling loss Qw is equal to or more than the given determination value. Therefore, the control portion is functionally achieved to determine whether or not the coolant W flows through the fifth and sixth coolant circulation paths 85 and 86 into which the radiator 50 is incorporated. In the present embodiment, the thermostat 60 and the ECU 1 correspond to a flow control device.

Next, effects of the cooling device 100 will be described. In the cooling device 100, the thermostat 60 is closed in the cold state (for example, the coolant temperature THW is equal to or lower than 75 degrees Celsius). For this reason, the coolant W flows through the coolant circulation paths 81, 82, and 83 in the cold state in the cooling device 100. Further, each of the coolant circulation paths 81, 82, and 83 does not include the radiator 50. Thus, basically, the coolant W flowing through the engine main body 21 is not cooled in the radiator 50 in the cold state, in the cooling device 100. This enhances the warm-up characteristics of the engine 20, in the cooling device 100.

Also, in the cooling device 100, the coolant W flows through the communication path 24 and the bypass path 23 formed in the engine main body 21, after the coolant W flowing through the coolant circulation path 83 flows through the water-cooled header 30. For this reason, in the cooling device 100, the heat transferred to the coolant W from the exhaust gas via the water-cooled header 30 in the cold state can be utilized to warm the engine 20. This further enhances the warm-up characteristics of the engine 20. As a result, the cooling device 100 enhances the warm-up characteristics of the engine 20 as compared to a cooling device 100X, as illustrated in FIG. 10.

On the other hand, the thermostat 60 is opened in the warm state in the cooling device 100. For this reason, the coolant W flows through the fourth to sixth coolant circulation paths 84, 85, and 86 in the warm state. Each of the fifth and sixth coolant circulation paths 85 and 86 includes the radiator 50. Thus, the coolant W cooled by the radiator 50 in the warm state is pressure-fed by the water pump 10 in the cooling device 100. For this reason, the water-cooled header 30 included in the sixth coolant circulation path 86 can be cooled in the cooling device 100. This can prevent or suppress overheating or boiling of the coolant W. In other words, the cooling device 100 can satisfy both of the improvement of the warm-up characteristics of the engine 20 and the prevention or the suppression of overheating or boiling of the coolant W.

On the other hand, the heat capacity of the water-cooled header 30 is smaller than that of the engine main body 21 in the cooling device 100. Thus, the influence of the received heat on the water-cooled header 30 is greater than that on the engine main body 21, the influence being made on the flowing coolant W, in the cooling device 100. Also, the flow rate of the coolant W flowing through the water-cooled header 30 is changed in response to the opening or closing state of the thermostat 60, as illustrated in FIG. 11, in the cooling device 100. Specifically, the flow rate of the coolant W flowing through the water-cooled header 30 in the cold state where the thermostat 60 is closed is lower than that in the warm state where the thermostat 60 is opened. This is because the coolant W flowing through the water-cooled header 30 flows through the third coolant circulation path 83 when the thermostat 60 is closed and the pressure loss of the coolant W flowing through the bypass path 23 included in the third coolant circulation path 83 is significant.

For this reason, in the cooling device 100, for example, in cases where the engine 20 drives in the high-load driving such as the full throttle just after the cold stating, the amount of heat transferred to the water-cooled header 30 might suddenly increase in spite of the small heat capacity and the small flow rate of the flowing coolant W. Therefore, the coolant W might be overheated or boiled within the water-cooled header 30 before entering the engine main body 21.

In this regard, the ECU 1 operates according to a flowchart illustrated in FIG. 12, in the cooling device 100. Additionally, this flowchart is repeated at a short interval during the driving of the engine 20. The ECU 1 determines whether or not the thermostat 60 is closed (step S1). When the determination is negative, this flowchart is finished once, because a special process is not needed. In contrast, when the determination is affirmative in step S1, the ECU 1 determines whether or not the cooling loss Qw is equal to or more than a given determination value (step S2).

When the cooling loss Qw is equal to or more than a given determination value, it is determined that the coolant W might be overheated or boiled in the water-cooled header 30. Thus, when the determination is negative in step S2, this flowchart is finished once. In contrast, when the determination is affirmative in step S2, the ECU 1 controls the thermostat 60 to forcibly open (step S3). Therefore, the control to forcibly open the thermostat 60 is performed as illustrated in FIG. 13. Further, this can prevent or suppress the overheating of the coolant W in the water-cooled header 30, even if the received heat suddenly increases in the water-cooled header 30.

Also, when the ECU 1 estimates the cooling loss Qw, generally, the ECU 1 can detect the cooling water temperature THW, the intake air temperature THA, the rotational number NE, and the intake air quantity GA by the use of the sensors which have already been equipped in. For this reason, when the environmental state where the water-cooled header 30 is used is investigated, the cooling device 100 has an advantage in cost as compared with cases where a sensor directly detects the temperature of the coolant W flowing through the water-cooled header 30 or the temperature of the exhaust gas. Also, when the environmental state of the water-cooled header 30 is investigated by the use of the direct detection sensor mentioned above, the thermostat 60 is forcibly opened after an increase in received heat amount is actually detected. In this case, this might result in an insufficient responsiveness to the sudden increase in received heat amount. In contrast the responsiveness of the cooling device 100 is superior to the above case.

On the other hand, as for a small heat capacity of the water-cooled header 30 in the cooling device 100, the orifice 70 is provided in the downstream of the water-cooled header 30 and the front side of the joining point of the fifth and sixth coolant circulation paths 85 and 86, as mentioned above. For this reason, the flow rate of the coolant W in the upstream of the orifice 70 is decreased as illustrated in FIG. 14 in the cooling device 100, and the pressure of the coolant W is increased by the amount of the decreased flow rate.

The pressure force of the coolant W increases, as the coolant temperature THW increases. In the cooling device 100, however, the pressure force P2 of the coolant W in the coolant outlet 304 of the water-cooled header 30 is stronger than the pressure force P1 in the coolant inlet 303 by about 50 KPa, as illustrated in FIG. 15. For this reason, the cooling device 100 can raise the boiling point of the coolant W in the water-cooled header 30, thereby preventing or suppressing the boiling of the coolant W in the water-cooled header 30 in the warm state. Also, the orifice 70 has only to be provided. Therefore, this can avoid a complicated configuration, as compared with cases where electric-type flow control valves are respectively provided in the engine main body 21 and the water-cooled header 30 as cooled objects and the flow rates of the coolant W flowing through the cooled objects are individually controlled. Thus, the cooling device 100 can prevent and suppress the damage of the engine 20 due to the overheat or the boiling of the coolant W in the water-cooled header 30.

The above embodiment is an example suitable for the present invention. The present invention is not limited to the above-mentioned embodiment, and other embodiments, variations and modifications may be made without departing from the scope of the present invention. For example, the above embodiment has described the water-cooled header 30, which is the exhaust system cooling portion, having a specific structure as illustrated in FIG. 2. However, the present invention is not limited to the above structure. The exhaust system cooling portion may have another arbitrary structure capable of cooling the entirely or a part of the exhaust manifold.

Also, for example, the above embodiment has described the water-cooled header 30 which is the exhaust system cooling portion. This is because the catalyst for cleaning the exhaust gas is arranged near the engine 20 to cool the exhaust gas flowing into the catalyst. However, the present invention is not limited to the above configuration. The exhaust system cooling portion may have another configuration which can cool exhaust gas before flowing into the catalyst by the use of the cooling medium.

Also, for example, the above embodiment has described the thermostat 60 and the ECU 1 which are the flow control portion. This is because, to control the flow of the coolant W, the thermostat 60 which can switch whether or not the coolant W is allowed to flow through the radiator 50 on the basis of the opening and closing states of the thermostat 60 is useful, and such a configuration is also advantageous in consideration of the costs. However, the present invention is not limited to the above configuration. For example, a pipe communicating the radiator 50 with the water pump 10 may be provided, and in addition a switching portion, such as an electromagnetic valve, which can switch whether or not the coolant W is allowed to flow through the pipe may be provided. So, the electromagnetic valve, instead of the thermostat 60, is the object to be controlled by the ECU 1, and the electromagnetic valve in the closed state is forcibly opened instead of the thermostat 60. Therefore, the coolant W is made to flow through the radiator 50 while bypassing the thermostat 60. In this case, the electromagnetic valve and the ECU 1 correspond to the flow control portion.

Also, for example, the above embodiment has described plural coolant circulation paths 81 to 86 as the plural coolant circulation paths. However, the present invention is not limited to the above configuration. The number of the plural coolant circulation paths may be changed as necessary.

Also, for example, the above embodiment has described the cases where the coolant W is controlled by determining whether or not the coolant W is allowed to flow through the fifth and sixth coolant circulation paths 85 and 86 on the basis of a given determination value. This is because the thermostat 60 and the ECU 1 correspond to the flow control portion. Further, such a configuration can cool the coolant at a higher flow rate, thereby further suppressing the overheating or the boiling due to a sudden increase in the heat transferred to the water-cooled header 30. However, the present invention is not limited to the above configuration. For example, the coolant W may be allowed to flow only through the sixth coolant circulation path 86 including the water-cooled header 30 among the fifth and sixth coolant circulation paths. After that, the coolant W may be allowed to flow through the fifth coolant circulation path 85. In this case, the coolant W can be cooled in a stepwise manner if needed. Also, this can cool the coolant W while ensuring the warm-up characteristics of the engine 20.

Specifically, the joining point of the fifth and sixth coolant circulation paths can be provided, a bypass pipe can be provided in the fifth coolant circulation path 85 to bypass the radiator 50, and a switch portion, such as an electromagnetic valve, can be provided for switching whether the coolant W flows through the bypass pipe or the radiator 50. And the electromagnetic valve and the thermostat 60 are the objects controlled by the ECU 1. Further the electromagnetic valve is controlled to flow the coolant W through the bypass pipe when the thermostat 60 is forcibly opened. This can allow the coolant W to flow only through the sixth coolant circulation path 86 among the fifth and sixth coolant circulation paths 85 and 86. After that, the electromagnetic valve can be controlled such that the coolant W flows through the radiator 50, thereby also allowing the coolant W to flow through the fifth coolant circulation path 85. In this case, for example, plural determinations values including a first determination value and a second determination value larger than the first determination value are employed as given determination values. Also, the thermostat 60, the electromagnetic valve, and the ECU 1 correspond to the flow control portion in this case.

The above embodiment also has described the orifice 70 incorporated into the sixth coolant circulation path 86. This is because the boiling of the coolant W can be prevented or suppressed in the warm state. However, the present invention is not limited to the above configuration. For example, the orifice 70 may be provided in the downstream of the water-cooled header 30 and on the front side of the engine main body 21 in the third coolant circulation path 83. In this case, this can prevent or suppress the boiling of the coolant W due to a sudden increase in the heat transferred to the water-cooled header 30 in the cold state. The above embodiment also has described the orifice 70 corresponding to the flow rate adjusting portion. However, the present invention is not limited to the above configuration. For example, the flow rate adjusting portion may be an electronic flow rate adjusting valve. For example, the ECU 1 appropriately controls the flow rate adjusting valve to increase the pressure force of the coolant W in the water-cooled header 30 depending on the situation or to adjust the pressure force of the coolant W in the water-cooled header 30 according to the necessity. Further, the flow rate adjusting valve can be controlled in such a way, for example, based on the degree of the cooling loss Qw or in response thereto.

It is also reasonable that various portions such as a detection portion, an estimation portion, and a control portion employed in the present invention are achieved by the ECU 1 which mainly controls the engine 20. However, these portions may be achieved by a hardware such as another electronic controller, a special electronic circuit, or a combination thereof. For example, the flow control portion according to the present invention may be achieved as a module combining the thermostat 60 and a special electronic circuit acting as the control portion. 

1. An engine cooling device comprising: a cooling medium pressure-feeding portion feeding a common cooling medium to plural cooling medium circulation paths; an engine including an engine main body incorporated into at least one of the plural cooling medium circulation paths; an exhaust system cooling portion incorporated into at least one of the plural cooling medium circulation paths, and cooling an exhaust system of the engine by use of the coolant, a heat capacity of an exhaust system cooling device being smaller than that of the engine main body; a cooler incorporated into at least one of the plural cooling medium circulation paths, and cooling the coolant; a flow control device determining whether or not the cooling medium flows through the at least one of the plural cooling medium circulation paths into which the cooler is incorporated on the basis of a given determination value, and controlling a flow of the cooling medium, wherein the given determination value relates to an amount of heat transferred from the exhaust gas to the cooling medium in the exhaust system cooling portion.
 2. The engine cooling device of claim 1, further comprising a flow rate adjusting portion incorporated into at least one of the cooling medium circulation paths into which the exhaust system cooling portion is incorporated, among the plural cooling medium circulation paths, and adjusting a flow rate of the cooling medium discharged from the exhaust system cooling portion such that a pressure force of the cooling medium flowing through the exhaust system cooling portion is greater than a system pressure force of the cooling medium flowing through each of the plural cooling medium circulation paths. 